The assessment of the criticality of raw materials allows the identification of the likelihood of a supply disruption of a material and the vulnerability of a system (e.g. a national economy, technology, or company) to this disruption. Inconclusive outcomes of various studies suggest that criticality assessments would benefit from the identification of best practices. To prepare the field for such guidance, this paper aims to clarify the mechanisms that affect methodological choices which influence the results of a study. This is achieved via literature review and round table discussions among international experts. The paper demonstrates that criticality studies are divergent in the system under study, the anticipated risk, the purpose of the study, and material selection. These differences in goal and scope naturally result in different choices regarding indicator selection, the required level of aggregation as well as the subsequent choice of aggregation method, and the need for a threshold value. However, this link is often weak, which suggests a lack of understanding of cause-and-effect mechanisms of indicators and outcomes. Data availability is a key factor that limits the evaluation of criticality. Furthermore, data quality, including both data uncertainty and data representativeness, is rarely addressed in the interpretation and communication of results. Clear guidance in the formulation of goals and scopes of criticality studies, the selection of adequate indicators and aggregation methods, and the interpretation of the outcomes, are important initial steps in improving the quality of criticality assessments.

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BACKGROUND
The aim of the present research was to provide a strategy for the start‐up of upflow anaerobic sludge blanket (UASB) reactors treating sugar cane vinasse, with emphasis on the relevant sulfur compounds along the reactor height. To this end, a laboratory‐scale UASB reactor was started up and its performance under the applied conditions was studied.

RESULTS
Biomass was able to assimilate organic loading rates from 3 to 10 kg chemical oxygen demand (COD) mR−3 d−1, reducing VFAs accumulation, while increasing biogas production rate (BPR) from 0.92 to 4.12 m3 mR−3 d−1. The COD and sulfate (SO42−) were mainly removed in the reactor bed, showing homogenous distribution in the blanket and settler zones. However, from bottom to top of the reactor, a slight decrease of total and free sulfide concentrations was observed, indicating that the sludge bed in the UASB reactor was exposed to H2S concentrations higher than those measured in the reactor effluent.

CONCLUSIONS
During 54 days, the development of macroscopic granules, the COD removal efficiency, the BPR and the CH4 content proved good indicators to monitor the start‐up period. Further research will be needed for strategy validation in pilot and full‐scale UASB reactors treating vinasse.@en

In recent decades, academia has elaborated a wide range of technological solutions to recover water, energy, fertiliser and other products from municipal wastewater treatment plants. Drivers for this work range from low resource recovery potential and cost effectiveness, to the high energy demands and large environmental footprints of current treatment-plant designs. However, only a few technologies have been implemented and a shift from wastewater treatment plants towards water resource facilities still seems far away. This critical review aims to inform decision-makers in water management utilities about the vast technical possibilities and market supply potentials, as well as the bottlenecks, related to the design or redesign of a municipal wastewater treatment process from a resource recovery perspective. Information and data have been extracted from literature to provide a holistic overview of this growing research field. First, reviewed data is used to calculate the potential of 11 resources recoverable from municipal wastewater treatment plants to supply national resource consumption. Depending on the resource, the supply potential may vary greatly. Second, resource recovery technologies investigated in academia are reviewed comprehensively and critically. The third section of the review identifies nine non-technical bottlenecks mentioned in literature that have to be overcome to successfully implement these technologies into wastewater treatment process designs. The bottlenecks are related to economics and value chain development, environment and health, and society and policy issues. Considering market potentials, technological innovations, and addressing potential bottlenecks early in the planning and process design phase, may facilitate the design and integration of water resource facilities and contribute to more circular urban water management practices.

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Society requires a stable and secure supply of raw materials. Raw materials supply stability and security are, amongst others, addressed by the concept of raw materials criticality, which focuses on the vulnerability of an economic unit (most commonly a country or region, but also the world, specific sectors, companies or products) to supply restrictions of certain mineral raw materials (cf. Schrijvers et al., 2020). The idea of keeping materials in the economic cycle for longer is specified in the Circular Economy (CE) concept, which encompasses efforts that reduce waste and improve material efficiency (Ellen McArthur Foundation, 2013; European Commission, 2018). So far, CE beyond recycling has not played a prominent role in the criticality debate. At the same time, critical raw materials (CRM) have only been a minor topic in the discussion on CE (recent exceptions include European Commission, 2018, and Gaustad et al., 2018). If properly aligned, criticality assessments might help in defining priority materials for the CE, and circularity strategies could substantially mitigate supply risks. In this paper, we explore the potential benefits, as well as caveats, of adopting a CE approach to CRM, based on our own experiences and our discussions organized by the IRTC (International Round Table on Materials Criticality) project.@en

This paper guides decision making in more sustainable urban water management practices that feed into a circular economy by presenting a novel framework for conceptually designing and strategically planning wastewater treatment processes from a resource recovery perspective. Municipal wastewater cannot any longer be perceived as waste stream because a great variety of technologies are available to recover water, energy, fertilizer, and other valuable products from it. Despite the vast technological recovery possibilities, only a few processes have yet been implemented that deserve the name water resource factory instead of wastewater treatment plant. This transition relies on process designs that are not only technically feasible but also overcome various non-technical bottlenecks. A multidimensional and multidisciplinary approach is needed to design water resource factories (WRFs) in the future that are technically feasible, cost effective, show low environmental impacts, and successfully market recovered resources. To achieve that, the wastewater treatment plant (WWTP) design space needs to be opened up for a variety of expertise that complements the traditional wastewater engineering domain. Implementable WRF processes can only be designed if the current design perspective, which is dominated by the fulfilment of legal euent qualities and process costs, is extended to include resource recovery as an assessable design objective from an early stage on. Therefore, the framework combines insights and methodologies from different fields and disciplines beyond WWTP design like, e.g., circular economy, industrial process engineering, project management, value chain development, and environmental impact assessment. It supports the transfer of the end-of-waste concept into the wastewater sector as it structures possible resource recovery activities according to clear criteria. This makes recovered resources more likely to fulfil the conditions of the end-of-waste concept and allows the change in their definition from wastes to full-fledged products.

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Food waste represents the largest fraction of the municipal solid waste generated in Europe and its management is associated to suboptimal performance in environmental, health, and social dimensions. By processing detailed multi-fold local data as part of a comprehensive and broadly understandable sustainability framework, this study quantifies the environmental and socio-economic impacts of household food waste management in the Amsterdam Metropolitan Area based on priorities set by local stakeholders. Five alternative short-term management options have been assessed against the current system, relying on poor separate collection and incineration. Four options involve separate collection of food waste followed by biological treatments (home/centralised composting and anaerobic digestion) while one involves a mix of separate collection and centralised mechanical-biological treatment followed by anaerobic digestion. Among these, separate collection followed by anaerobic digestion coupled with effective nutrient and energy recovery is, according to our findings, the preferred option to improve the sustainability of the current system in all dimensions considered, except for the economic pillar due to the collection costs. Home and centralised composting as well as mechanical-biological treatment are associated to more adverse impacts based on our findings. The study informs local stakeholders and authorities on the potential consequences of their options, thereby allowing them to make sound choices for a future waste and circular economy strategy.@en

Waste management represents a challenge for public authorities due to many reasons such as increased waste generation following urban population growth, economic burdens imposed on the municipal budget, and nuisances inevitably caused to the environment and local inhabitants. To optimize the system from a sustainability perspective, moving the transition towards a more circular economy, a better understanding of the different stages of waste management is necessary. A review of recently developed sustainability frameworks for waste management showed that no single framework captures all the instruments needed to ultimately provide a solid basis for comprehensive analyses of the potential burdens associated with urban waste management. Bearing this limitation in mind, the objective of this research is to propose a conceptual and comprehensive sustainability framework to support decision-making in waste management of European cities. The framework comprises a combination of methods capable of identifying future strategies and scenarios, to assess different types of impacts based on a life cycle perspective, and considers the value of waste streams, the actors involved, and possible constraints of implementing scenarios. The social, economic, environmental, technical and political domains are covered, and special attention is paid to impacts affecting foremost the local population.@en

BACKGROUND: Microbial community dynamics during the anaerobic digestion of vinasse has been little studied. However, having knowledge about it is essential for early detection of reactor operational difficulties to apply preventive actions. This research studies the microbial community dynamics in the anaerobic digestion of vinasse, linking to experimental observations about product yields and organic matter degradation. RESULTS: Methane and sulfide yields decreased with increasing SO₄ ^2-/COD ratio, while the fraction of organic matter degraded by sulfate reducing bacteria increased from 4.5 ± 0.3% to 27.1 ± 0.6%. The archaeal community showed that acetoclastic Methanosaetaceae were little affected by the increase of the SO₄ ^2-/COD ratio, in contrast to the Methanomicrobiales and Methanobacteriales population, which decreased during the experiment. The total bacterial diversity was influenced mainly by substrate composition, showing that the increase of the SO₄ ^2-/COD ratio above 0.10 shifted the bacterial community to a lower richness. CONCLUSION: These results provide knowledge on the dynamics of the microbial communities, which can be useful to control the anaerobic digestion of sulfate-rich vinasses, showing that reactor stability equates to the higher ratios between total methanogens and total bacteria gene copy numbers, whereas operational difficulties can be associated to lower bacterial richness and higher community organization.

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The treatment of vinasse in lagoons causes methane emissions during the anaerobic decomposition of the organic matter. The recovery of this methane, to produce renewable energy in anaerobic digestion power plants (ADPPs) replacing fossil fuels and reducing greenhouse gas emission, could bring environmental benefits. The aims of this work were: (1) to compare alternatives of ADPPs available for the treatment of vinasse; and (2) to evaluate the impacts of ADPPs as alternative for lagooning Cuban vinasse; both by means of Life Cycle Assessment (LCA) and exergy analysis (EA). The LCA and EA showed that the ADPPs improve the environmental profile with respect to the lagooning of vinasse, reducing up to 77% the total score and recovering up to 46% of the exergy extracted from the natural environment during the process, respectively. The highest environmental benefits for the ADPPs were observed when the subprocesses biogas production from raw vinasse, sulfide removal by biooxidation with air oxygen addition and energy generation in spark ignition engines were used. In that case, the treatment of 1072 ton of vinasse (exergy content of 740.6 GJ_ex) can produce 175 GJ_ex as "electricity and heat", 191 GJ_ex as "wastewater for fertirrigation", 21.7 GJ_ex as "digestate", and 0.41 GJ_ex as "sulfur in the filter cake". This way, the produced 1.3 million cubic meters of vinasse (1.34·10⁶ ton/year) reported by the Cuban Ministry of the Cane Sugar Industry can replace 485263 GJ_ex per year as energy and bio-fertilizers, reducing the negative environmental impacts for the studied categories.

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